n.
Invisible gas consisting of vaporized water .
When mixed with minute droplets of water, it has a white, cloudy appearance. In nature, steam is produced by the heating of underground water by volcanic processes and is emitted from hot springs , geysers , fumaroles , and some volcanoes . Steam also can be generated on a large scale by technological systems, such as those using fossil-fuel-burning boilers and nuclear reactors. Modern industrial society relies on steam power; water is heated to steam in power plants, and the pressurized steam drives turbines that produce electric current : thermal energy is converted to mechanical energy, which is converted into electricity.